The California couple arrested for torturing their 13 children kept the kids shackled to their beds for months at a time as punishment — for “infractions” that included washing their arms, investigators said Thursday.

“If the children were found to wash their hands above the wrist area they are accused of ‘playing in the water’ and they would be chained up,” Riverside County District Attorney Mike Hestrin said at a press conference.

“These punishments would last for weeks or even months at a time.”

The conditions in David and Louise Turpin’s horror house suggest the siblings — aged 2 to 29 — were often not let out of their shackles to use the bathroom, he added.

In abuse that spanned decades, the Turpins at first used ropes to tie their kids up, but graduated to “chains and padlocks” when one of the children managed to escape the bonds.

When police arrived Sunday — after a 17-year-old daughter escaped out of a window and called 911 — three of the siblings, aged 11, 14 and 22, were chained up, although the parents managed to free two of them while the cops were at the door, Hestrin said.

The parents also subjected their kids to “frequent” beating and strangulation as punishment, he said.

David and Louise Turpin face up to life in prison for torture, child abuse and neglect. They will go before a judge for the first time later Thursday.